You may request a currently unassigned call sign under the Vanity Call Sign System that was previously assigned to you as your primary, secondary, repeater, auxiliary link, control or space station. You do not have to wait two years after expiration to request your previously held vanity call sign.
If you are filing for a call sign that was not issued as a vanity, considered to be a request by a former holder, that callsign may be from any callsign Group. That is, you do not have to hold a specific class of operator license.
For other sequenially issued calls, the FCC does require that you were the previous license holder within 2 years from the date of your application or be able to provide evidence of holding that call sign if you are asked for it.
A call sign requested by a former holder may be from any call sign region.